Hello! To share libraries, you also need to share the assets that are referenced by the libraries. For example: if you have all your assets inside a folder "res://assets", and you want to share the library, I'd recommend putting the library file and the assets folder inside a folder. To your new project, add a copy of that assets folders, such that you again have "res://assets" and paste the library file(s) into the library directory. This is the userdata folder by default, but you can change it to be the resource directory res://, in Project Settings -> AssetPlacer -> Settings -> Library Save Location. This way, you can have the assets folder and the library files next to each other.
Hope this helps!